Sectional electrostatic sound producer



, Feb. 9, 1932. v. F. GRI-:AVES

SECTIONAL ELECTROSTATIC SOUND PRODUCER Fi1ed`Jan. 14. 1929 2 Sheets- Sheet l "zzaxzrasaza Feb. 9, 1932. v. F. GREAvEs 1,844,219

SECTIONAL ELECTROSTATIC SOUND PRODUCER Filed Jan. 14, 1929 2 Sheets-Sheet 2 Patented Feb. 9, 1932 UNITED STATES PATENT or-fries" vALENmnm r. GnnAvEs, or sr. oHAnLEs, rumors, Avss'IeNon.' 'ro narran :moms PATENTS conroArIomcr s'r. ummm-Immers, A couronner; or

NEVADA snc'rIoNAL mcrnosrarrc SOUND imminenzaV Application led Ianuary14,`1929. Seria-i No. 332,464'.

'The present invention relates to theelec trostatic or condenser type of sound produce or reproducer or loud speaker.

Among the objects ofhe invention is to J .provide anovelspeak'er of any desired size andstrength' and' composed of sections or units of such capacities, reactances and impedances as to produce large volumes of sound. without distortions and other defects peculiar to single large condenser structures.

Merely increasing the sige or area of a con'-" denser or electrostatic type of sound reproducer for the purpose of obtaining a greater or larger volume of sound, introduces unfav- 15-orab1e tone quality results. The present invention coxnprehendsthe provision of a large volume condenser or electrostatic type of speaker in which the desirable tone qualities lof a small area electrostatic or condenser type 2 0 of speaker are retained as well as improved,

1 and the unfavorable characteristics of asin,-

gle equally large device are eliminated.

If a single verylarge condenser speaker be Y connected-to a vacuum tube of usual type, the impedance relations are such as to produce the unfavorable tone qualities. mentionedl condenser. It may be represented 'by the formula 'L 85 1 where o is QnrX the frequency of the electromotiveforce and c is the capacity of the condenser, the capacity being directly propor-i tional to the area of the condenser. `From this it will become apparentthat this react.

ance diminishes with increasing frequency so that at high frequencies 'the reactance 'be-v pedance of thevacuum tube. This results inI unfavorable and undesirable frequency characteristics for the reproduction of audible sounds.' The higher frequencies will be lacking in loudness or volume, and the result is a comes smallin comparison with the plate im-v booming effect of reproduction with poor or no articulation of speech. My invention avoids such disadvantagesj by the building up of a lar e area electrostatic or condenser speaker roma number of small units and- '55 connecting them electrically in either parallel or series relations, or both, or in any combination thereof with or without. resistances and reactances` b oth inductive and capacitive to form anfelectrical network afordingin -anyfl case the optimum reproduction quality under any conditions and with any type of amplifier. x If, for example, a'large area speaker be made or` composed of two or more smaller condensers, and they be connected electrically- 65 in series, the effective capacity is smaller than that of a single condenser of the total area, and a more favorable frequency characteristic isproduced. To illustrate, ina speaker divided into two parts or sections which are connected electrically in series, the capacity would be one fourth that of the large single condenser speaker, as also of a large condenser speaker with the sections electrically connected in parallel.V `Another object'ofthe"m5 invention is to so connect the units orsections as to secure the desired large volume of sound -with proper and favorable -tone qualities and characteristics.

-A further object is to maintain a 'constant large direct electromotive -force or polarizing voltage between theplates of the condenser,

so as to secure proper operation efects. The units ares'o arranged that they may be effectively in series qwith respect tothe alternating L signal voltage and effectively in parallel with respect to the direct polarizing voltage. l 4

.Other advantages, objects, capabilities and features are comprehended by the 'invention-zum aswill later appear and as areinherentl possessed thereby.

Referring to the drawings, Fig. 1 is a view partly in elevationfand partly broken -away to show a mode'of forming a speaker` from units or sections.y

Fig. 2 is a sectionalvview taken ina plane represented by line 2 2 'in Fig.` 1 ofthe drawings. v i

Fig. 3 is-a transverse sectional view taken" 110 in a plane shown by line 3-3 in Fig. 1 of the drawings.

Fig. 4 shows a series of units connected in line.

Fig. 5 shows a number of units connected both longitudinally and laterally.

Fig. 6 is a' diagramatic showing of the circuits used when connecting two units in series, and

Fig. 7 is a similar diagramatic showing of the circuits for connecting three units in series.

Referring now more in detail to the drawings, each unit or sect-ion comprises a metal plate portion 1 which is preferably, but not necessarily, curved or convex and having undulations on the convex or outer surface thereof. These undulations comprise crests 2, troughs 3 and slopes 4 between the crests and troughs. Slots 6 may be provided in the troughs and adjacent portions of the slopes as clearly shown in Figs. 1 and 2.

At the edges or margins of the plate are provided inwardly extending flanges 7, 8, 9 and 10, provided with one or more apertures or slots 11, 12, 13 and 14 through which suitable securing elements, such as rivets or bolts 15 may extend when securing together the flanges of adjacent sections or units.

At the margins of the plate and in the'inner surface thereof are provided recesses or grooves 16 into which extend marginal portions of a dielectric sheet 17 carrying on its outer surface a flexible conducting medium 18. The dielectric may be a sheet of rubber,

or silk, or rubberized silk or any other like and similar material which may be specially treated as desired. The flexible conducting medium may be a metal or metallized film or coating, or foil such as gold, silver, copper, aluminum or similar -metal foil, suitably made to adhere to the outer surface of the dielectric 17. In the slots or grooves 16 are forced or pressed binding or anchoring elements 19 which may be in the form of wire, rods, or the like, and if desired may be of conducting material. These elements permanently hold or anchor the marginal portions of the flexible dielectric. In the case of the coating thereon extending into the. grooves 16, and the rods being of conducting material, these rods contacting with the conducting medium will afforda convenient means for the connecting of circuit conductors thereto. lVhen a woven fabric is used as a dielectric or as a part of a dielectric, such as rubberized silk, it. is prefrable to dispose the threads of the fabric on a bias or diagonally to the sides and ends of the unit and toa tensioning member later described, whereby the sheet will be properly stretched and without wrinkles.

At an intermediate partof the unit, the plate is provided with a transverse slot 2() located between inwardly extending flanges 21 and 22 connected with a web 23 in which .disposed a tensioning bar 26 which may be of insulating material. To this bar are secured connecting elements 27 and 28 such as4 wires with outer bent ends or hooks, these elements extending inwardly through the slot 2O and the vrespective apertures or slots 24 and 25, the inner ends of these elements being suitably connected to the4 free end portions 29 and 30 of a leaf spring 31 secured at its intermediate portion to a boss 32 forming an integral part of the web 23, as clearly shown in Figs. 2 and 3. The spring portions 29 and 30 impress tension on elements 27 and 28 which in turn press the bar 26 inwardly to deflect a part 33 of the dielectric and conductor film 17 18 into the groove 20 as clearly shown in Fig. 2. This tensioning is 'effective thereon throughout the length of the' bar 26 and stresses the fabric in a direction on a bias or diagonally to the threads of the fabric thus producing a tensioning in at least two directions from a single line of tension stress application. This maintains the dielectric properly stretched whereby all chance of any wrinkle is eliminated.

Under the electrostatic stresses imposed upon the dielectric, the portions thereof between crests, are ieXed to fand from the slopes and troughs of the plate, thus setting up sound waves in the air.

The yunits are so constructed that they may be connected together in any desired number and into any desired form and finalsize of the speaker. As forexample, in Fig. 4 the units are shown as connected in a line with the flange 9 of one unit bolted to the flange 10 of another. Fig. 5 shows the connecting of the units also laterally, as by bolting the flange 7 of one unit to the fiange 8 of another. In this way a large volume speaker may be built-up without the' defects and disadvantages that would be present in a speaker of similar size but being a single Ccondenser.

Referring to Figs. 6 and 7, the speaker may be connected to `a vacuum tuber35 having the usual electrodes, such as plate36, grid 37 and filament 38. The filament has a heating source such as an A- battery 39, connected to the filament by conductors 40 vand41. Input leads or conductors 42 and Y43 are connected respectively to conductor 40` and v-gr1d 37. From the\plate 36 runs aconductor 44 to a resista-nce 45 or` primary 4 6. F1g. 7) 4of an audio transformer 47, andthence to a potential source, such as a v13 battery 48, the negative side of which connects. by a conductor 49 to the conductor 40. j y

In Fig. 6 are shown two speaker units 50 and 51 connected electrically capacitively in series, and having back plates 52 and 53 and front plates 54 and 55. The opposite ends of the resistance are connected by conductors 56 and 57 by way of condensers 58 and 59 and conductors 60 and 61 to the back plate 52 of unit 50 and the front platex55 of thev unit 51, respectively. The front plate 54 of unit and the back late 53 of unit 51 are connected by way `o a conductor 62, condenser 63 and conductor 64. vThe capacities of the condensers 58 and 59 are preferabl considerably greater than those of the ea er units. Plates 52 and 53 are connecte in parallel with resistances 65 and 66,and by Way of conductors 67 and 68 to a polarizing voltage pole 69. Likewise plates 54 and 55 are con-.- nected in parallel with resistances 70 and 71,

and 'by way of conductors 72 vand 73 `to a polarizing voltage' pole 74. Theresistances 65, 66, 70, and 71 may be ofthe order of one half me hom. The polarizing voltage or` potential is applied between the poles 69 and 74, and may 4be supplied from any suitable source, as a battery or high voltage rectifier,

as desired. n v

In Fig. 7 the circuit is shown as extended to ajspeaker having three units 75, 76 and 77 respectively havingl back plates 78, 79,'and 80, V'and front plates` 81, 82, and 83. An end of a secondary 84 of the transformer 47 is connected by way of conductor .85, condenser 86 and conductor 87 to the back platel 7 8 of the unit 75. The other end of the secondary 84 is connected by way ofa conductor 88 to front plate 84 of unit 77. Front plate 81 of unit 75 is -connected by way of conductor 89, condenser 90. and conductorV 91 to back plate 79 of unit 76, and front plate 82 of -unit`7 6 is connected by way of conductor 92, condenser '93 andconductor 94 to -back plate of unit 77 v l Back plates 78, 794 and 80 are connected in parallel withresistances 95, 96 and 97, by conductors 98, 99 and 100. These resistances are connected by conductors'101, 102 and 103 to a common-point- 104 connected by'av conductor105 to a polarizing vtoltage pole 106.

Front plates 81, 82 and 83 are connected in arallel with resistances 107, 108 and 109 and y way 'of .conductors 110, 111 and112,the

resistances being connected by way oiconductors 113, 114 and 115 to a common point 116 which is connected by a: conductor'117 to another polarizing voltage pole 118.y The' values of the resistances and the condensers iii-.these circuits are preferably of thesame order as those shown Fig. 6. y

Between the poles 106 and 118 is connected a potential or voltage source, whichfin the case shown is `a high voltage rectiiier, shown i'n thedotted line area.- This rectifier has an in ut line 119-120 having an All. supply, w 'ch may be of 6 0 cycles or the like, and connected to a r'nnary 121 of a step-up transformer 122. e transformer may have@ heating secondary 123 connected by conducin the diagram of tors 124 and 125 to a lament 126 of a triode vacuum tube 127. y. The grid'128 and plate 129 may be connected together by conductors 130 and 131, so that the tube will function asa diode rectifier. The conductors 130 and 131 are connected by a conductor 132 to the `p01@ 106. y The transformer has -a high potential secondary 133 connected at one end by way of.'

1. An electrostatic sound producer coini prisingunits each having a rigid conductor, a flexibleconductor, a dielectric therebetween,

y and means for connecting the units together to form a large area producer assembly, the rigid conductorcf y' one unit being capacitively connected to the flexible conductor of another unit.

2. n "electrstaticisound producer com-- prising units each having a conductor, a iexible conductor, adielectric therebetween, v 'y each unit having projections, land means for connecting a 'projection of one unit to an adjacent projection of another unit,`the rigid imo conductor of one unit being capacitively con- 'A Z nected tothe flexible conductor of another unit.

3. -An electrostatic sound producer com'- i vprising units each having a rigid conductor,v

a flexible conductor, a dielectric therebetween, the rigid'conductor of one lunit being capacitively connected to the flexible conductor of another unit', polarizing potential l poles connected in parallel to said conductors.

4. An electrostatic sound producer comi prising units each having a rigid conductor, a flexible conductor, a dielectric therebetween, the rigid conductor of one unit being capacitively connected to the iiexible conductor of another unit, polarizing potential poles, Aone of said poles being resistantly connected to the' rigid lconductors of said units, and the-12 other Iof said poles being resistantl)7 connected -to the ilexible conductors of said units.

5.. An electrostaticl sound producer coinprisingunits each having a rigid conductor,

a flexible conductor, a dielectric therebetween, the rigid conductor of one unit being capaci- *tively connected to'the'- flexible conductor of another unit, polarizing potential poles, a resistance connected to each flexible conductor `of said units and to one of said poles, and a las ` between the conductors, the front conductor Y of each unit being connected capacitively to the back conductor of the next unit of the series, polarizing potential poles, the front c conductors of the series being connected to one of said poles', and the back conductors of .the series being connected to the other of said poles.

8. An electrostatic sound producer comprising a series of units each having back and front conductors of which one is movable under electrostatic stresses, vand a dielectric between thelconductors, the front conductor 0f each unit being connected capacitively to the back conductor of the next unit of the series, polarizing potential poles, said poles respectively connected to said front and said back conductors'of said series, and resistances in the connections from said poles to said conductors.

In Witness whereof, I hereunto subscribe my name to this specication.

VALENTINE F. GREAVES. 

